Non-woven filtration media suitable for multi-layer thermally bonded filter elements are generally known. Such nonwoven filtration medias are commonly prepared by a mechanical carding process followed by thermally bonding the carded fibrous web with a bicomponent fiber or binder. A bicomponent fiber is a fiber that has an outer sheath layer of one polymer and an inner core made of another polymer. The outer sheath layer is usually constructed of a polymer with a lower melting point than the inner core material. The use of bicomponent fibers in a nonwoven carded fiber mat allows the lower outer sheath layer to melt when exposed to heat in an oven, while the inner core material does not melt in the same temperature conditions. The outer sheath layer melts and wicks between fibers to thermally bond fibers together where they intersect in the fiber mat. The outer sheath material thus forms a thermal bonding material, while the inner core material remains solid providing strength and structure to the filter media.
Laminated, multi-layer filter elements including bicomponent fibers and/or binder materials are also known in the art. For example, non-woven filter elements constructed with a mix of staple and bi-component fibers are described in U.S. Pat. No. 5,827,430 entitled “Coreless and spirally wound non-woven filter element,” the entire disclosure of which is hereby incorporated by reference in its entirety. Strips of a nonwoven filter material including both staple fibers and bicomponent fibers are wound together under compression and thermally bonded to form a laminated, multi-layer filter element. Additional filters and methods relating to laminated, multi-layer filter elements are described in U.S. Patent Pub. Nos. 2011/0210059 and 2014/0275692, the entire disclosures of which are hereby incorporated by reference in its entirety.
However, when used in some applications, such as filtration at elevated temperatures or in chemically aggressive environments, a typical multi-layered filtration media is limited in chemical compatibility and temperature capability by the lowest melt temperature and chemical compatibilities of the different polymers in the bicomponent fiber. Thus, when the temperature or chemical capabilities of either polymer are exceeded, the filtration media can break down in use, resulting in decreased life span of the filter.
Filter media and filter constructions with improved resistance to challenging operating conditions is desired. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.